Eli Wallach was almost poisoned on the set after drinking acid used to burn the bags filled with gold coin to make them rip open easier when struck with the spade. The acid had been poured into a lemon soda bottle and Wallach didn't know it. He drank a lot of milk and filmed the scene with a mouth full of sores.

In addition to the train scene, Eli Wallach cheated death in the first scene where Blondie shoots him down from a hanging. The gunshot scared the horse, which took off running at full speed for nearly a mile. Wallach's hands were tied behind his back, and he had to hang on for dear life with his knees.

Sad Hill Cemetery was a very-convincing set piece constructed by the pyrotechnic crew and not a real cemetery. Today the site is marked as a local point of interest. Though the central stone 'proscenium' and parapet are gone, the circles of grave-mounds are still quite prominent.

Four scenes were cut from the original English-language release and were never dubbed into English from Italian. When American Movie Classics showed the "Extended English Version", the scenes were restored. Clint Eastwood and Eli Wallach dubbed their voices for the movie, but another actor had to be found to dub Angel Eyes' lines, as Lee Van Cleef had died in 1989. The actor that dubbed Angel Eyes's lines into English was voice actor Simon Prescott.

The three man gunfight scene is called either a "Mexican standoff" or a truel (game theory). There are several mathematical papers covering the many complex outcomes of a truel. Other movies that use a truel are Reservoir Dogs (1992) and Pulp Fiction (1994).

Eli Wallach remembered that when he first came to Madrid all the hotels were full. Clint Eastwood invited him to sleep over at a friend's house and they shared the same bed. Wallach's wife Anne Jackson told him he could boast that he was the only man to sleep with Clint Eastwood.

The three principal actors are the only ones who speak actual English in the film: Clint Eastwood, Lee Van Cleef, Eli Wallach, with the exceptions of Al Mulock (the one-armed man) and John Bartha (the sheriff). Everyone else in the film is really speaking their native language, mostly Italian and Spanish, and was later dubbed into English.

Sergio Leone originally titled his story "The Magnificent Rogues" and "The Two Magnificent Tramps," but impulsively changed it during a meeting in which he was pitching the story to United Artists executives Arnold Picker and Arthur Krim. The improvised new title amused them both, and they agreed to put between $1.2 and $1.6 million to make it and retain North American distribution rights.

After Eli Wallach agreed with Sergio Leone that Tuco would carry his pistol on a lanyard, the director asked him to grasp the gun by shaking his neck, thus making the gun land in his hand. Wallach claimed that he wasn't able to do the intended action, and asked Leone to demonstrate it. When Leone tried, the pistol missed the director's hand and hit his crotch. Leone then told Wallach to hold the gun in the belt.

Charles Bronson was offered both the roles of Tuco and Angel Eyes (the latter because Sergio Leone feared that audiences would not take kindly to Lee Van Cleef going from the fatherly, likable Col. Mortimer to a sneering villain. He declined both.

When Blondie and Angel Eyes are traveling to the cemetery, Blondie shoots a skulker, then counts the number of people that will be traveling together. He says, "Six. A perfect number." In mathematics, a number is perfect if the sum of its factors (excluding itself) equals itself. Six is a perfect number because 1, 2, and 3 are factors and 1 + 2 + 3 = 6. (The next perfect number is 28.)

The grips on Clint Eastwood's pistol have an inlaid silver rattlesnake. His pistol in For a Few Dollars More (1965) had the same grips. In the TV series Rawhide (1959), Rowdy Yates (Eastwood) kills a gunfighter carrying a pistol with the same grips and takes it for his own. Eastwood's character would carry the pistol with the rattlesnake grips for the remainder of the series' run.

In the theatrical trailer, Angel Eyes is "The Ugly" and Tuco "The Bad," which is the reverse of their designations in the actual film. This is because the Italian title translated into English is actually The Good, the Ugly, the Bad, not The Good, the Bad and the Ugly, and the Italian trailer had "The Ugly" and "The Bad" in that order. When the trailer was transferred to English, The Ugly and The Bad were not reversed to coincide with the altered title, causing the incorrect designations.

Eli Wallach claims that Sergio Leone decided that Tuco would carry his pistol on a lanyard and stuck in his belt rather than a holster because Wallach told him he always had trouble putting a pistol in a holster without looking at it.

In 1960's Hollywood was still following the The Motion Picture Production Code of 1930 (a.k.a. The Hays Moral Code), especially when it came to Westerns. After the Good, the Bad and the Ugly was released Hollywood had to change its moral standards in order to stay competitive with such foreign made films. This particular film broke many if not most of those standards.

As an Italian-made film, the sound would not recored live. This means that the actors would have spoken whatever they wanted and the dialogue would have been dubbed in post production. This was the traditional way of making films in Italy and was because of the poor sound proofing in their studios and the difficulty of keeping Italian crews and spectators quiet. All the actors in the film spoke in their native languages, and were dubbed into other languages in post-production (Italian, German, Spanish, English etc.)

The film was shot with a process called Techniscope. This process means that you can shoot without an anamorphic lens, and only use half as much film as you would normally use. The Techniscope process places two widescreen frames on a single 35 mm frame. This technique is called "2-perf". A 35mm frame has 4 perforations.

The Union prison camp "Battleville" was inspired by the actual Confederate prison camp of Andersonville, where thousands of Union prisoners died, and based on steel engravings of Andersonville from August 1864. In the film, when Angel Eyes (disguised as a Union sergeant) is berated by the camp commandant about his treatment of Confederate prisoners, he sarcastically asks the commandant if Union soldiers are treated any better in Andersonville.

Though no specific year or date is stated in the movie, at least part of it takes place during the New Mexico Campaign of 1862. This is confirmed when both the hotel-keeper and Tuco mentions the retreating Confederate General Sibley (the historical Henry H. Sibley) and the advancing Union Colonel Canby (another historical person, Edward Canby). This is consistent with the campaign that took place between February-April 1862 in the Union Territory of New Mexico and the Confederate State of Texas.

After the scene where Blondie splashes water in Tuco's face in the infirmary, there is a fade-out to the next scene. This was where the intermission was located, but this fade-out was excised in the 179-minute extended version.

Although Sergio Leone never made an official sequel to this film, screenwriter Luciano Vincenzoni wrote a treatment for a sequel, tentatively titled 'Il buono, il brutto, il cattivo n. 2.' According to Eli Wallach, the film would have followed Tuco pursuing Blondie's grandson for the gold. Clint Eastwood expressed an interest in acting as a narrator for the film; Joe Dante and Leone were approached to direct and produce the film respectively. The project was eventually vetoed by Leone, as he did not want the film's title, nor its characters, to be reused.

The trim on Confederate soldiers' uniforms identified the type of unit they were assigned to. Blue indicated infantry, gold cavalry and red artillery. Most of the soldiers in the prison camp wore historically accurate uniforms.

In two of the deleted scenes featuring Lee Van Cleef's character, a substitute voice actor - Simon Prescott, was used for the dubbing. Van Cleef had died in 1989, and the scenes had never been dubbed into English.

Tuco tells his brother Father Pablo Ramirez (played by Luigi Pistilli) "Where we came from, if one did not want to die of poverty, one became a priest or a bandit!". Ironically, in For a Few Dollars More (1965), Pistilli played a bandit, so in a sense, he's been both a priest and a bandit at the same time.

The train features an armed car with a mortar type cannon. These were actually mounted on trains during the Civil War, especially where railroads had to operate near places where there was heavy fighting.

Shortly after Blondie brings in Tuco to the Sheriff for the first time, the Sheriff comes out with one of Tuco's wanted posters and unrolls it to show Tuco his picture on it. If you look carefully, you will see that the name on the poster is 'Guy Calloway' (presumably one of Tuco's aliases). Guy Calloway also happens to be the name of one of the wanted men that Col. Mortimer (played by Lee Van Cleef who played Angel Eyes in this movie) shoots and kills in For a Few Dollars More (1965).

For the scene where Angel Eyes interrogates Maria the prostitute for information about Bill Carson, Lee Van Cleef was appalled by the fact that he was required to actually hit Maria's actress, Rada Rassimov, complaining "I can't hit a woman." Rassimov replied with "Don't worry. I'm an actress. Even if you slap me for real, it's no problem," but Van Cleef further stated "I know, but I can't!" As a result, a stunt double was used for shots where Rassimov was slapped, which were intercut with shots of Van Cleef himself. As he later put it: "There are very few principles I have in life, and one of them is I don't kick dogs, and the other one is I don't slap women in movies.'

The town where Tuco's second hanging takes place, the town where Maria is interrogated by Angel Eyes, the town where Tuco visits the gun shop, and the town where Tuco and his gang attempt to ambush Blondie during a cavalry march are, in fact, the same town. Set designer Carlo Simi had previously created the set for For a Few Dollars More (1965) (where the town was referred to as El Paso), and was portrayed as four different settlements in The Good, the Bad and the Ugly (1966) by shooting in different areas of the set for each scene. The 'El Paso' set still exists today, as a Western theme park known as 'Mini Hollywood.'

In the scene where Blondie brings a tied-up Tuco into town to claim the bounty on him, Tuco spits out a cigar and yells out something in Spanish. Translated to English, he is yelling out "Son of a bitch that gave birth to you!"

The mud-strewn town where Blondie brings Tuco for his first hanging is the same town from Sergio Corbucci's Django (1966), filming for which had taken place earlier that year. The set, built on the Elios Film Studios in Rome, had not been cleaned between its use in the two films.

According to Eli Wallach, when it came time to blow up the bridge, Sergio Leone asked the Spanish army captain in charge to trigger the fuse, as a sign of gratitude for the army's collaboration. They agreed to blow up the bridge when Leone gave the signal "Vai!" (Go!) over the walkie-talkie. Unfortunately, another crew member spoke on the same channel, saying the words "vai, vai!", meaning "it's OK, proceed" to a second crew member. The captain heard this signal, thought it was for him and blew the bridge; unfortunately, no cameras were running at the time. Leone was so upset that he fired the crewman, who promptly fled from the set in his car. The captain was so sorry for what happened that he proposed to Leone that the army would rebuild the bridge to blow it up again, with one condition: that the fired crewman be re-hired. Leone agreed, the crewman was forgiven, the bridge was rebuilt and the scene was successfully shot.

During the scene right before the final duel where Tuco (Eli Wallach) is running frantically through the cemetery, a dog can be seen running on-screen at the beginning of the scene. In reality, that was improvised on the spot. Sergio Leone, who was afraid that the scene was going to slip into melodrama, released the dog without informing Eli Wallach first - thus, his look of surprise is quite genuine.

When the bridge is blown up, and Tuco and Blondie are hunkered down behind sandbags waiting for the explosion, Clint Eastwood's career came within 2 feet of ending prematurely. A fist-sized piece of rock shrapnel from the explosion slams into the sandbag right next to Eastwood's head (watch it in slow motion to see the rock flying in).

Although Blondie (Clint Eastwood) is labeled "the good" in the film, he actually kills 11 people during the course of the movie, which is more than Tuco (Eli Wallach) and Angel Eyes (Lee Van Cleef) combined. Tuco, "the ugly", kills 6 people while Angel Eyes, "the bad", has the lowest body count with 3.

Mario Brega appears in all 3 of the Dollars Trilogy movies as a henchman for the main villain(s), and in all 3 movies, his character meets an unfortunate demise (oddly enough, none of these deaths is caused by gunfire). In this movie, his character of Wallace is killed when Tuco (chained to him) jumps off the train with him, and bangs his head against some rocks. This is the only movie from the trilogy in which Brega plays an American, whereas in the other movies, he plays a Mexican.

Despite being frequently referred to as a sequel to For a Few Dollars More (1965) ("For a Few Dollars More"), this film is set during the American Civil War whereas that one takes place afterwards, and while Lee Van Cleef here plays a villain who gets killed, he turns up there as a very much alive good guy.